I. Field of the Invention
The present invention relates to data communication. More particularly, the present invention relates to a novel and improved multi-state power control mechanism for use in a wireless communication system.
II. Description of the Related Art
A modern day communication system is required to support a variety of applications. One such communication system is a code division multiple access (CDMA) system that supports voice and data communication between users over a terrestrial link. The use of CDMA techniques in a multiple access communication system is disclosed in U.S. Pat. No. 4,901,307, entitled “SPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERS,” and U.S. Pat. No. 5,103,459, entitled “SYSTEM AND METHOD FOR GENERATING WAVEFORMS IN A CDMA CELLULAR TELEPHONE SYSTEM.” Another CDMA system is disclosed in U.S. patent application Ser. No. 08/963,386, entitled “METHOD AND APPARATUS FOR HIGH RATE PACKET DATA TRANSMISSION,” filed Nov. 3, 1997, now U.S. Pat. No. 6,574,211, issued Jun 3, 2003 to Padovani et al., (hereinafter referred to as the HDR system). These patents and patent application are assigned to the assignee of the present invention and incorporated herein by reference.
CDMA systems are typically designed to conform to one or more standards. Such standards include the “TIA/EIA/IS-95-B Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System” (the IS-95 standard), the “TIA/EIA/IS-98 Recommended Minimum Standard for Dual-Mode Wideband Spread Spectrum Cellular Mobile Station” (the IS-98 standard), the standard offered by a consortium named “3rd Generation Partnership Project” (3GPP) and embodied in a set of documents including Document Nos. 3G TS 25.211, 3G TS 25.212, 3G TS 25.213, and 3G TS 25.214 (the W-CDMA standard), and the “TR-45.5 Physical Layer Standard for cdma2000 Spread Spectrum Systems” (the cdma2000 standard). New CDMA standards are continually proposed and adopted for use. These CDMA standards are incorporated herein by reference.
In a CDMA system, communication between users is conducted via one or more base stations. A first user on one remote terminal (e.g., a cellular phone) communicates with a second user on a second remote terminal by transmitting data on the reverse link to a base station. The base station receives the data and may route the data to another base station. The data is transmitted on the forward link of the same base station, or a second base station, to the second remote terminal. The forward link refers to transmission from the base station to a remote terminal and the reverse link refers to transmission from the remote terminal to a base station. In CDMA systems, the forward and reverse links are typically allocated different frequencies.
On the reverse link, each transmitting remote terminal acts as interference to other active remote terminals in the network. The reverse link capacity is thus limited by the total interference that each remote terminal experiences from other transmitting remote terminals.
To reduce interference and increase the reverse link capacity, the transmit power of each remote terminal in the IS-95 system is controlled by two power control loops. The first power control loop adjusts the transmit power of the remote terminal such that the signal quality, as measured by the energy-per-bit-to-noise-plus-interference ratio, Eb/(No+Io) of the signal received at the base station is maintained at a particular threshold or level. This level is referred to as the power control setpoint (or simply, the setpoint). The second power control loop adjusts the setpoint such that a desired level of performance, as measured by the frame-error-rate (FER), is maintained.
A power control mechanism for the reverse link is disclosed in detail in U.S. Pat. Nos. 5,056,109 and 5,265,119, both entitled “METHOD AND APPARATUS FOR CONTROLLING TRANSMISSION POWER IN A CDMA CELLULAR MOBILE TELEPHONE SYSTEM,” assigned to the assignee of the present invention, and incorporated by reference herein.
In some CDMA systems, such as the HDR system, data transmission from the remote terminal may not be continuous (i.e., bursty). In particular, the data transmission may be characterized by bursts of data transmission separated by periods of silence (i.e., no transmission). During the silence periods, no data transmission is available to adjust the setpoint. However, the operating conditions of the remote terminal may have changed (e.g., due to movement of the remote terminal). Thus, the transmit power level last used by the remote terminal may not be sufficient to achieve an error-free transmission when data transmission restarts.
As can be seen, techniques that can be used to adjust the transmit power level of a remote terminal in a communication session characterized by non-continuous data transmission are highly desirable.